In high-performance two-stroke engines, it is known to provide expansion chamber exhaust systems. Such exhaust systems can include an exhaust port, a header section connected to the exhaust port, a divergent section connected to the header section, and a convergent baffle section. When the exhaust port is opened, a high pressure pulse travels through the header section and the divergent section. When the pulse reaches the convergent baffle section, it is reflected back toward the exhaust port. Such systems also include a tail pipe, from which the exhaust is delivered from the exhaust pipe to the atmosphere.
In expansion chamber exhaust systems, at a given engine speed, the arrival time of a reflected pulse at the exhaust port, relative to the phase of the combustion cycle of the engine, has a substantial effect on engine performance. The travel time of the reflected pulse is determined by the distance from the exhaust port to the convergent baffle section, or the "tuned length", and is designed to match one predetermined engine speed. However, at high engine speeds, the required tuned length is shorter than the required tuned length at low engine speeds.
Further, it is know to extend the range of engine speed over which useful power is developed by constructing the convergent baffle section with an elongated profile, resulting in reflected pulses of a longer duration. However, such pulses have a lower amplitude, and thus, a lower maximum engine power.